For object detection, conventionally, a capacitive touch sensor sequentially scans all the traces one by one from the first trace to the last trace, as shown in FIG. 1. As shown in the left part of FIG. 1, a capacitive touch sensor 10 includes a substrate 12 and traces X1-Xm and Y1-Ym printed thereon. The substrate 12 may be a glass plate, a plastic membrane, or a printed circuit board (PCB), and the traces X1-Xm and Y1-Ym are patterns made of metal, indium-tin oxide (ITO) film, or other conductive materials. As shown in the right part of FIG. 1, the capacitive touch sensor 10 will scan the traces X1-Xm and Y1-Ym one by one, each time when it performs a scanning process for object detection. For example, during the time period of T0-T1, only the trace Y1 is scanned; during the time period of T1-T2, only the trace Y2 is scanned; and so on.
However, for a large size touch panel, the sequential scanning process needs a very long overall scanning time for completing the scanning of all the traces. On the other hand, noise 14 from the external or from a current source always affects the signals detected from the traces X1-Xm and Y1-Ym. Since noise radiation is time-varying and each of the traces X1-Xm and Y1-Ym is scanned at a different time in the sequential scanning process, the noise radiation will impart non-uniform effect on the analog-to-digital conversion (ADC) values of the traces X1-Xm and Y1-Ym that are derived from the detected signals from the traces X1-Xm and Y1-Ym.
Therefore, it is desired a circuit and method capable of reducing noise interference and shortening an overall scanning time of a capacitive touch sensor.